A tandem type color printer conventionally well known in the art includes a main frame and a photosensitive unit. The photosensitive unit integrally supports a plurality of photosensitive drums and is configured to be slidably movable with respect to the main frame. More specifically, the photosensitive unit in the art includes a pair of metal plates, a positioning shaft, and a pair of resin frames. The pair of metal plates is adapted for supporting the plurality of photosensitive drums at its axial ends so that the plurality of photosensitive drums is disposed between the pair of metal plates. Each of the pair of metal plates has a front end portion (an end portion positioned downstream of another end portion in a mounting direction) formed with a notched portion. The positioning shaft extends in a leftward/rightward direction and bridges between rear end portions of the pair of metal plates. The pair of resin frames is adapted for supporting the front and rear end portions of the pair of metal plates.
The main frame is provided with a pressure member and a reference shaft extending in the leftward/rightward direction. The pressure member provided in the main frame presses the positioning shaft rearward, so that the notched portions formed in the front end portions of the pair of metal frames are brought into abutment with the reference shaft provided in the main frame. Thus, the photosensitive unit is positioned with respect to the main frame.